My nephew was taken and tempory placed with a cousiin, been a year now, and my sister hasn't changed.Me being the only blood relitive do I have rights

I want to adopt him, but 1st I have to gardianship which was granted to cousin. My sister has made no attempt to do anything to get him. The cousin won't let him see us nor let him come visit us. Like grandparents rights, is there any rights that can get so he can come to our house and see and visit us every so often...especially holidays, birthdays, ect..